In this paper, we proposed a method of canopy reconstruction and measurement based on 3D super resolution range-gated imaging. In this method, high resolution 2D intensity images are grasped by active gate imaging, and 3D images of canopy are reconstructed by triangular-range-intensity correlation algorithm at the same time. A range-gated laser imaging system(RGLIS) is established based on 808 nm diode laser and gated intensified charge-coupled device (ICCD) camera with 1392´1040 pixels. The proof experiments have been performed for potted plants located 75m away and trees located 165m away. The experiments show it that can acquire more than 1 million points per frame, and 3D imaging has the spatial resolution about 0.3mm at the distance of 75m and the distance accuracy about 10 cm. This research is beneficial for high speed acquisition of canopy structure and non-destructive canopy measurement.

Moving target detection is important for the application of target tracking and remote surveillance in active range-gated laser imaging. This technique has two operation modes based on the difference of the number of pulses per frame: stroboscopic mode with the accumulation of multiple laser pulses per frame and flash mode with a single shot of laser pulse per frame. In this paper, we have established a range-gated laser imaging system. In the system, two types of lasers with different frequency were chosen for the two modes. Electric fan and horizontal sliding track were selected as the moving targets to compare the moving blurring between two modes. Consequently, the system working in flash mode shows more excellent performance in motion blurring against stroboscopic mode. Furthermore, based on experiments and theoretical analysis, we presented the higher signal-to-noise ratio of image acquired by stroboscopic mode than flash mode in indoor and underwater environment.

A method of ns-scaled time-gated fluorescence lifetime imaging (TFLI) is proposed to distinguish different fluorescent substances in forensic document examination. Compared with Video Spectral Comparator (VSC) which can examine fluorescence intensity images only, TFLI can detect questioned documents like falsification or alteration. TFLI system can enhance weak signal by accumulation method. The two fluorescence intensity images of the interval delay time tg are acquired by ICCD and fitted into fluorescence lifetime image. The lifetimes of fluorescence substances are represented by different colors, which make it easy to detect the fluorescent substances and the sequence of handwritings. It proves that TFLI is a powerful tool for forensic document examination. Furthermore, the advantages of TFLI system are ns-scaled precision preservation and powerful capture capability.

An automatic fishing net detection and recognition method for underwater obstacle avoidance is proposed. In the method, optical gated viewing technology is utilized to obtain high-resolution fishing net images and extend detection distance by suppressing water backscattering and background noise. The fishing net recognition is based on the proposed histograms of slope lines (HSLs) descriptors plus a support vector machine classifier. The extraction of HSL descriptors includes five steps of contrast-limited adaptive histogram equalization, the Gaussian low-pass filtering, the Canny detection, the Hough transform, and weighted vote. In the proof experiments, the detection distance of the fishing net reaches 5.7 attenuation length and the recognition accuracy reaches 93.79%.

Laser range-gated imaging has great potentials in remote night surveillance with far detection distance and high resolution, even if under bad weather conditions such as fog, snow and rain. However, the field of view (FOV) is smaller than large objects like buildings, towers and mountains, thus only parts of targets are observed in one single frame, so that it is difficult for targets identification. Apparently, large FOV is beneficial to solve the problem, but the detection range is not available due to low illumination density in a large field of illumination matching with the FOV. Therefore, a large field-of-view range-gated laser imaging is proposed based on image fusion in this paper. Especially an image fusion algorithm has been developed for low contrast images. First of all, an infrared laser range-gated system is established to acquire gate images with small FOV for three different scenarios at night. Then the proposed image fusion algorithm is used for generating panoramas for the three groups of images respectively. Compared with raw images directly obtained by the imaging system, the fused images have a larger FOV with more detail target information. The experimental results demonstrate that the proposed image fusion algorithm is effective to expand the FOV of range-gated imaging.

Underwater 3D range-gated imaging can extend the detection range over underwater stereo cameras, and also has great potentials in real-time high-resolution imaging than 3D laser scanning. In this paper, a triangular-range-intensity profile spatial correlation method is used for underwater 3D range-gated imaging. Different from the traditional trapezoidal method, in our method gate images have triangular range-intensity profiles. Furthermore, inter-frame correlation is used for video-rate 3D imaging. In addition, multi-pulse time delay integration is introduced to shape range-intensify profiles and realize flexible 3D SRGI. Finally, in experiments, 3D images of fish net, seaweed and balls are obtained with mm-scaled spatial and range resolution.

Underwater range-gated laser imaging (URGLI) still has some problems like un-uniform light, low brightness and contrast. To solve the problems, a variant of adaptive histogram equalization called contrast limited adaptive histogram equalization (CLAHE) is proposed in this paper. In experiment, using the CLAHE and HE to enhance the images, and evaluate the quality of enhanced images by peak signal to noise ratio (PSNR) and contrast. The result shows that the HE gets the images over-enhanced, while the CLAHE has a good enhancement with compressing the over-enhancement and the influence of un-uniform light. The experimental results demonstrate that the CLAHE has a good result of image enhancement for target detection by underwater range-gated laser imaging system.

Three-dimensional super-resolution range-gated imaging (3D SRGI) is a new technique for high-resolution 3D sensing. Up to now, 3D SRGI has been developed with two range-intensity correlation algorithms, including trapezoidal algorithm and triangular algorithm. To obtain high depth-to-resolution ratio of 3D imaging, coding method was developed for 3D SRGI based on the trapezoidal algorithm in 2011. In this paper, we propose the range-intensity coding based on the triangular algorithm and the hybrid range-intensity coding based on the triangular and trapezoidal algorithms. The theoretical models to predict the maximum coding bin number are developed for different coding methods. In the models, the maximum coding bin number is 7 for three coding gate images under the triangular algorithm, and the maximum is extended to 16 under the hybrid algorithm. The coding examples of 7 bins and 16 bins mentioned above are also given in this paper. The comparison among the three coding methods is performed by the depth-to-resolution ratio defined as the ratio between the 3D imaging depth and the product of the range resolution and raw gate image number, and the hybrid coding method has the highest depth-to-resolution ratio. Higher depth-to-resolution ratio means better 3D imaging capability of 3D SRGI.

Three-dimensional super-resolution range-gated imaging has been developed for high-resolution 3D remote sensing with two range-intensity correlation algorithms under specific shapes of range-intensity profiles (RIP). However, pulsed lasers have a minimum pulse width which limits range resolution improvement. Here a spatial difference shaping method is proposed to break the resolution limitation. This method establishes a shaping filter, and the pre-reshaping gate images are reshaped by spatial difference and yield new gate images with the laser pulse width equivalently narrowed as half value which improves the range resolution. Furthermore, the boundary blurring caused by non-rectangular laser pulses are also eliminated.

Three-dimensional range-gated imaging is a new 3D sensing technique with higher resolution than 3D flash LIDAR,
and has great potential in realizing high-resolution real-time 3D imaging to satisfy land surface remote sensing
applications. In this paper, three existing approaches of realizing 3D range-gated LIDAR are introduced including their
advantages and disadvantages. Among them, the two methods of gain modulation and range-intensity correlation can
reconstruct a 3D scene from two gate images, which enable 3D flash imaging. We propose a 3D superresolution
range-gated flash LIDAR based on triangular algorithm of range-intensity correlation, and further present a coding
method based on triangular algorithm for high depth-to-resolution ratio. Some prototyping experiments and simulations
are demonstrated.

High-resolution real-time three-dimensional imaging is important in 3D video surveillance, robot vision, and
automatic navigation. In this paper, a three-dimensional superresolution range-gated imaging based on inter-frame
correlation is proposed to realize high-resolution real-time 3D imaging. In this method, a CCD/CMOS with a gated
image intensifier is used as image sensor, and depth information collapsed in 2D images is reconstructed by
spatial-temporal inter-frame correlation with a resolution of about 1000×1000 full-frame pixels within a frame.
Furthermore, under inter-frame correlation a 3D point cloud frame is generated at video rates corresponding to
CCD/CMOS utilized. Finally, some proof simulation experiments are demonstrated.

The range-gated laser imaging technology has become a useful technique in many applications in recent years. In
order to expand the range of imaging detection and improve the measurement range resolution of the imaging system, we
used circular step advance delay sequence for the synchronous control. And we developed a method of using dynamic
phase-shift technique in FPGA to improve the precision of the delay in the time sequence, which can make the precision
of the delay stepper between the two adjacent frames less than global clock period of the FPGA and approach the limit of
FPGA’s operating frequency. That is to say, it can equivalently increase the clock frequency. Then we can effectively
improve measurement range resolution of the imaging system. In this paper, we have studied how dynamic phase-shift
technique can be equivalent to higher clock frequency and performed some experiments. We presented the structure of
dynamic phase-shift technique used to improve the precision of delay in the synchronization control time sequence. And
the simulation and experimental results are showed in this paper. The results demonstrate that using dynamic phase-shift
technique in FPGA can make the precision of the delay between the ICCD’s trigger pulse and the laser’s trigger pulse
reach 1ns, which means the resolution of measurement range can be 0.15m theoretically. The timing control signal with
dynamic phase-shift technique designed in this paper can be widely used in range-gated imaging because of its high
timing control precision and flexible parameter setting.

Target acquisition is of great importance for ship borne range-gated night vision system which can achieve target finding,
target tracing and ranging. A digital image processing algorithm is developed for the mentioned night vision equipment
above. Target contour is extracted using Canny edge detection algorithm based on self-adapted Otsu threshold
segmentation. Furthermore, edge thinning, edge connection and morphologic methods are implemented to ameliorate the
acquired contour. Pixels inside the contour are collected utilizing horizontal-vertical traverse. After ship targets from
range-gated equipment being all tested, target contour and inner pixels can both be acquired through this algorithm.

Echo broadening effect (EBE) is inherent in three-dimensional range-gated imaging (3DRGI). The effect impacts the
range-intensity profile of gate images which is crucial in three approaches of 3DRGI based on depth scanning,
supperresolution depth mapping and gain modulation. In this paper, we give the space-time model of EBE which
illustrates three typical range-intensity profiles under different temporal parameters of laser pulse and gate pulse. A head
zone and a tail zone exist in both sides of the profiles. Our research demonstrates that EBE should be suppressed in depth
scanning and gain modulation methods and utilized in supperresolution depth mapping.

Coastal surveillance is very important because it is useful for search and rescue, illegal immigration, or harbor security and so on. Furthermore, range estimation is critical for precisely detecting the target. Range-gated laser imaging sensor is suitable for high accuracy range especially in night and no moonlight. Generally, before detecting the target, it is necessary to change delay time till the target is captured. There are two operating mode for range-gated imaging sensor, one is passive imaging mode, and the other is gate viewing mode. Firstly, the sensor is passive mode, only capturing scenes by ICCD, once the object appears in the range of monitoring area, we can obtain the course range of the target according to the imaging geometry/projecting transform. Then, the sensor is gate viewing mode, applying micro second laser pulses and sensor gate width, we can get the range of targets by at least two continuous images with trapezoid-shaped range intensity profile. This technique enables super-resolution depth mapping with a reduction of imaging data processing. Based on the first step, we can calculate the rough value and quickly fix delay time which the target is detected. This technique has overcome the depth resolution limitation for 3D active imaging and enables super-resolution depth mapping with a reduction of imaging data processing. By the two steps, we can quickly obtain the distance between the object and sensor.

Target tracking is of great importance in imaging system, which can be applied in surveillance, as well as salvage and rescue where 3D spatial coordinates are used to locate the target. Range-gated imaging system is capable of acquiring range information of targets. However, azimuth is also necessary to provide the spatial coordinates to achieve target tracking. This paper presents a target azimuth estimation method for range-gated imaging system, aiming at obtaining essential information for vision-based automatic tracking. Due to the noise and low contrast of range-gated image, median filter and histogram equalization are used. Then the Otsu method is performed to make the segmentation of target and background. After segmentation, morphologic transformation methods will be taken in order to delete false targets. With pixels of target extracted from the image, the centoid will be derived. Next the pinhole camera model is applied to work out the azimuth coordinate. Since the focus length of camera is needed in the formula, an NC (Numerical Control) zoom module is developed. In this module, a sliding potentiometer is connected to the focus motor in camera, which serves as a feedback of the focus. To read the focus length and control the focus motor, an MCU (with AD converter) is used. Once the target azimuth information is obtained, the pan-tilt control unit can track the target bit by bit automatically.

We present a method of target detection against strong light based on gate viewing. In this method, a nanosecond-scale
gate shutter is used to control the exposure time of CCD and reduce the collection of obtrusive light, and a
nanosecond-scale pulsed laser is used to illuminate targets and increase signal energy. By matching them, the ratio
between signal and obtrusive light will be significantly improved to detect targets against light disturbance. We have
analyzed the method in theory, and performed it in experiment. In addition, a stroboscopic time sequence is used, and the
setting of temporal parameters is also discussed.

We propose a surveillance photonic fence for night remote intrusion detection, especially in bad environmental
conditions. The photonic fence is established by the synchronization of a pulsed infrared laser and a gated imaging sensor.
Since the wavelength of the laser is invisible, the photonic fence is also invisible. Only when targets pass the fence, their
image information can be collected. Objects and backgrounds out of the fence are all filtered directly which decreases the
complexity of image processing about target extraction. For the fence, its location can be easily adjusted by the delay
time between the laser pulse and the gate pulse, and its thickness can be set by changing the gate time and the laser pulse
width. Furthermore, target space information can also be estimated in terms of the range information of the photonic
fence.

This paper presents a novel algorithm to extract signal area of range-gated images under the EBE effect. Besides
the histogram information, this algorithm uses average gray value information to select threshold with iterative
processing. With average gray value information, the edges of signal area can be segmented out accurately. The
algorithm can handle images under the impact of EBE effect, reduce the noise in the images and segment the
objects from the noise area effectively without many morphological operations which keeps the certain figure from
distortion. Experiment result shows that the algorithm is effective to the signal areas extraction of images under
EBE effect, signal areas can be segmented out accurately.

3D range-gated imaging with stepping delay is a novel technology developed in recent years. 3D timing control signal
based on delay line and logical AND gate technology is proposed innovatively in order to satisfy the distance precision
of centimeter of 3D imaging in complex background. 3D timing control signal is produced through FPGA nanosecond
timing generation module and picosecond timing adjustment module. Simulation and experiment show that the delay
precision of the timing signal designed in this paper is 150 picoseconds, and the narrowest pulse width is close to the
limitation of TTL signal (1ns level). The timing control signal designed in this paper can be widely used in 3D
range-gated imaging because of its high timing control precision, compact construction and flexible parameter setting.
Keywords: range-gated, picosecond, timing control, FPGA, delay line

We present a flash trajectory imaging technique which can directly obtain target trajectory and realize non-contact
measurement of motion parameters by range-gated imaging and time delay integration. Range-gated imaging gives the
range of targets and realizes silhouette detection which can directly extract targets from complex background and
decrease the complexity of moving target image processing. Time delay integration increases information of one single
frame of image so that one can directly gain the moving trajectory. In this paper, we have studied the algorithm about
flash trajectory imaging and performed initial experiments which successfully obtained the trajectory of a falling
badminton. Our research demonstrates that flash trajectory imaging is an effective approach to imaging target trajectory
and can give motion parameters of moving targets.

We have presented the Echo Broadening Effect of range-gated active imaging. It can respectively generate a head
signal part and a tail signal part both sides of the echo signal profile. Our research demonstrates that the head signal
and the tail signal impact the depth of view, detection range and imaging quality, especially the head signal. In order
to solve the problems, we establish a model of the echo broadening effect, and analyze the signal energy
characteristics and atmospheric backscatter. We have given the depth of view under the effect, verified it in
experiment, and found that the reasonable choosing of the illuminator laser pulse time and the camera gate time can
mange the effect to optimize range-gated imaging systems.

We design a new double-layer grating template, which has the advantages of period uniformity, period number adjustability and continuous period regulation. Under the new template, we research the relationship between the spectrum and the grating templates: the resonant wavelength is mainly determined by the grating period; the intensity of transmission peak loss lies in the external pressures; the bandwidth of transmission spectrum can be controlled by the period number. Therefore, various applications can be realized by optimizing the transmission spectrum by reasonably selecting the matched parameters.

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